An antenna that can produce independent beams in various directions, whilst the beams overlap on, or reuse, surfaces in the antenna has long been a goal of antenna research for a range of applications. One class of antenna of study in this regard is the reflector antenna with an array of feeds, where one feed is used for each beam. Such antennas can generate beams of high gain and low sidelobes within a limited range of directions. Considerable work has been undertaken in determining the multibeam capabilities of particular reflector configurations and in optimizing the sizes and shapes of reflector surfaces for desired sets of beams.
U.S. Pat. No. 4,298,877 issued to Sletten, C. J. on 3 Nov. 1981 and entitled “Offset-fed multibeam tracking system utilizing especially shaped reflector surfaces” describes a reflector-shaping process. This reflector-shaping process refers only to two beam directions. The antenna uses two separate subreflectors, one for each of the beams, and the beam directions are in the same plane as the feed and subreflector offsets. In the shaping procedure, the main reflector and one of subreflectors are first shaped to obtain an aperture distribution with uniform phase, low radiation-pattern sidelobes and maximum aperture efficiency or beam gain. The second subreflector is then shaped as a phase-correcting subreflector for producing the second beam. This procedure produces more than two beams without modification to the shapes of the reflector surfaces, by placing additional feeds in the focal regions of the two subreflectors. However, this approach disadvantageously results in greatly inferior performance in a desired application where a large number of beams and a large beam-direction range are required. In particular, maximum gain rapidly decreases, and sidelobes rapidly increase as additional feeds are added, because the reflector surfaces are not shaped to maximize the performance of all beams.